Power take-off unit with automatically actuated drag brake

Abstract

A power take-off unit includes a drag brake assembly that is automatically engaged when a hydraulically actuated clutch assembly is disengaged. The drag brake assembly includes a brake piston that is axially aligned with the output shaft and is urged into frictional engagement therewith by a spring. When pressurized fluid is provided, the clutch assembly is engaged to cause the output shaft to be rotatably driven by the input gear. At the same time, the pressurized fluid causes the brake piston to retract axially within the cylindrical recess against the urging of the spring. As a result, the brake piston is moved out of frictional engagement with the output shaft to permit free rotation of the output shaft. When pressurized fluid is not provided, the clutch assembly is disengaged to prevent the output shaft from being rotatably driven by the input gear. The lack of pressurized fluid in the clutch chamber to allows the spring disposed within the cylindrical recess to urge the brake piston axially into frictional engagement with the output shaft to retard rotation thereof.

What is claimed is:  
     
       1. A power take-off unit comprising: 
       an input gear;  
       an output shaft;  
       a clutch assembly connected between said input gear and said output shaft, said clutch assembly being operable in either an engaged condition, wherein said input gear is connected to drive said output shaft, or a disengaged condition, wherein said input gear is not connected to drive said output shaft, said clutch assembly being responsive to the application of pressurized fluid for being operated in said engaged condition;  
       a brake assembly being operable in either an engaged condition, wherein said brake assembly retards rotation of said output shaft, or a disengaged condition, wherein said brake assembly does not retard rotation of said output shaft, said brake assembly being responsive to the application of pressurized fluid for being operated in said disengaged condition; and  
       a conduit for selectively applying pressurized fluid simultaneously to both said clutch assembly and said brake assembly.  
     
     
       2. The power take-off unit defined in  claim 1  wherein said clutch assembly is normally maintained in said disengaged condition. 
     
     
       3. The power take-off unit defined in  claim 2  wherein said clutch assembly includes a spring that urges said clutch assembly to said disengaged condition. 
     
     
       4. The power take-off unit defined in  claim 1  wherein said brake assembly is normally maintained in said engaged condition. 
     
     
       5. The power take-off unit defined in  claim 4  wherein said brake assembly includes a spring that urges said brake assembly to said engaged condition. 
     
     
       6. The power take-off unit defined in  claim 1  wherein said clutch assembly is normally maintained in said disengaged condition, and wherein said brake assembly is normally maintained in said engaged condition. 
     
     
       7. The power take-off unit defined in  claim 6  wherein said clutch assembly includes a first spring that urges said clutch assembly to said disengaged condition, and wherein said brake assembly includes a second spring that urges said brake assembly to said engaged condition. 
     
     
       8. The power take-off unit defined in  claim 1  wherein said brake assembly includes a brake piston that is movable between an engaged position, wherein said brake piston engages said output shaft to retard rotation thereof, and a disengaged position, wherein said brake piston does not engage said output shaft to retard rotation thereof. 
     
     
       9. The power take-off unit defined in  claim 8  wherein said brake piston is co-axially aligned with said output shaft. 
     
     
       10. The power take-off unit defined in  claim 8  wherein said brake piston has a layer of a friction material secured thereto that engages said output shaft when said brake piston is moved to said engaged position. 
     
     
       11. The power take-off unit defined in  claim 8  wherein said brake assembly includes a spring for urging said brake piston to said engaged position. 
     
     
       12. The power take-off unit defined in  claim 11  wherein said spring is a wave spring.